Islam has been a part of life in what is now northern Nigeria for centuries, brought south hundreds of years ago by traders crossing the Sahara to swap gold and slaves with city states such as Kano, Borno and Katsina.
In 1804, an ethnic Fulani Islamic scholar, Usman Dan Fodio, led an Islamic jihad, overthrowing corrupt Hausa kings across the Sahel region, and establishing a caliphate, or religious government, in Sokoto, in the far northwest of modern-day Nigeria.
Sharia, the Islamic system of law banning alcohol and setting out strict punishments for everything from theft to sex outside marriage, was established and remained an integral part of the north.
When British colonial forces conquered the new rulers of the north at the end of the 19th century, they recognised the interests of the north by agreeing to separate legal codes for north and south, with many elements of Sharia retained in the northern penal code.
But they also put a halt to others, including banning stonings and amputations.
Since Nigeria gained its independence from Britain in 1960, demands have been growing for a return to full Sharia in the north and the issue has been hotly debated in a series of constitutional conferences from the late 1970s onwards.
In May last year, more than 15 years of military rule ended and a civilian government was sworn in. Last October, Governor Sani Ahmed of Zamfara State, a small state in northwest Nigeria, announced plans for Sharia.
Since then, three further states, including Kano, have declared Sharia and others are moving to do so.
Islamic leaders here say the movement has come from the demands of the Muslim majority in the north for a clean-up of society seen as having sunk under military rule.
"People believe the Sharia will improve the morals of society. Vices and corruption will cease," Kano State Chief Imam Sheikh Isa Waziri, who heads the Sharia Implementation Committee in the state, told AFP in an interview here Tuesday.
"Ninety percent of Kano people are Muslims and as Muslims they have to support Sharia. Sharia is sent by Allah. There is no going back," he said.
Many others, however, see the move to introduce Islamic law, on top of federal law, as more political than religious.
One of them is Bala Usman, a professor of history at Amhadu Bello University, Zaria. "The people behind the Sharia movement are politicians, not religious men. They feel the north lost out in last year's elections and want to create an alternative power structure, an alternative support," he said.
Another is Sheikh Ibrahim el-Zakzaky, an Islamist who has criticised Gov. Sani saying he is not a true Muslim and saying Sani was simply trying to build a base for his own ambitions.
But political commentators here say many ordinary northern Nigerians are disillusioned by years of misrule by secular military leaders and are ready to believe Islamic law can do more than secular law to curb problems of corruption and crime.
Aides to Kano State Governor Rabiu Kwankwaso, who Wednesday declared plans to introduce Sharia in Kano State, told AFP the governor had been a reluctant convert to the Sharia movement but felt obliged to accept it by popular pressure.
"This thing has started and it is very difficult now for any governor in the north to stop it," said one aide who asked not to be named.